With wireless communication devices in wireless communication systems, high efficiency has strongly been demanded from a viewpoint such as reduction in device size, and energy saving.
Power amplifiers in wireless communication devices are generally used at a high-efficiency saturation region. However, it has been recognized that in the event that a power amplifier is used around a saturation region, nonlinear distortion increases. As for a technique for reducing adjacent channel leakage power (Adjacent Channel Power, ACP) while suppressing this nonlinear distortion, there is distortion compensation processing. A distortion compensation apparatus configured to perform distortion compensation processing is included in wireless communication devices. As for distortion compensation apparatuses, there is a device employing a method such as series type or look up table (hereafter, referred to be as LUT) type, or the like.
On the other hand, with power amplifiers, it has been recognized that a phenomenon such as memory effect occurs. The memory effect is a phenomenon wherein, with a power amplifier, an output signal as to an input signal at certain point-in-time is influenced by an input signal in the past. Accordingly, a power amplifier has been desired wherein nonlinear distortion in the above power amplifier can be compensated, and also influence of memory effect in a power amplifier can be compensated.
Note that U.S. Pat. No. 7,561,636 has disclosed an example of a distortion compensation apparatus including multiple LUT. Also, Japanese Laid-open Patent Publication No. 2007-019782 has disclosed a technique for obtaining the offset of a distortion compensation coefficient stored in a LUT, and performing distortion compensation processing using a distortion compensation coefficient obtained by subtracting this offset.